1. Field of the Invention
The present invention relates to television tuners, and more particularly, to tuners used for reception of multiple channels.
2. Related Art
As televisions begin to incorporate the ability to receive digital, as well as analog broadcast signals, television tuners must offer improved performance and additional features at an attractive cost. An important specification for a tuner intended for digital terrestrial applications is immunity to strong interfering signals. These may be either unwanted television signals or signals from other sources. Another important specification is sensitivity, which is the lowest signal level that can be received with acceptable fidelity. An important feature that is often desired is the capability to receive two or more channels at once, for picture-in-picture (PIP) or personal video recording (PVR) capability.
There are various arrangements used in existing television systems to receive multiple channels at once. Either a passive splitter or an active splitter is used to provide inputs to two or more tuners. Passive splitters produce little distortion and give good immunity to unwanted interference, but they reduce the signal level driving each tuner and therefore reduce sensitivity. Active splitters (without pre-selection or automatic gain control) result in a low system noise figure and good sensitivity, but have significant distortion at high signal levels, and degrade immunity to strong interfering signals.
Furthermore, it may be required for the television to receive any combination of off-air and cable signals, up to the limit of the number of tuners. If one tuner is dedicated to off-air signals and another to cable signals, for example, this will not be possible.
Accordingly, there is a need in the art for a front end circuit configuration that provides pre-selection for off-air channels, AGC (automatic gain control), and switching capability for simultaneous reception of any combination of input signals, up to the number of tuners in the system.